recently running

[luketorjesen]

hey all, just got my 1980 gs850 running, but only under certain conditions. it wont idle without the choke on, and the petcock must set to prime or it wont run at all. thinking the fuel sending unit isnt working, can i put voltage across those wires to test it? if so, it def isnt working. was wondering if the choke thing could be the idle being set too low, or is it more likely a gas mix issue. the plugs went black shortly after i got it running. the previous owner put new jets in also. i know, lots of variables, but im merely a tenderfoot, so bear with me.

[Jaguarjoe]

I doubt if the fuel sending unit has anything to do with running the bike. It is only hooked up to the fuel level gauge.

[chef1366]

What mods did the PO jet the bike for?

[Steve]

Why did the PO change the jets? Does the bike have pods and/or a pipe?
These kinds of things are nice for us to know if you would like for us to help you diagnose problems.

Running only on prime sounds like a stuck petcock. It is possible to carefully take the vacuum diaphragm off and see if the o-ring that seals the fuel passage has gotten stuck in there. Mine had. I pulled it out of there carefully, stuck it back where it belongs and have had no problems since then.

Running only on choke is normal for the first minute or so. You should be able to feather the chock off after that, and the normal idle circuit will keep it going. If not, then the idle circuit (and, most likely, the rest of the carbs) needs a good cleaning.


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[luketorjesen]

ah vacuum diaphram, excellent, see when u buy a mystery bike for a hundred dollars, u tend to not know about things like vacuum hoses controlling the fuel, im sure i just pulled it off w/o seeing it and never replaced it. it was actually the PPO that did the jets, all i got from the PO was that it was to increase fuel. the PO put aftermarket air intakes on to increase airflow. as for the choke, ive tried feathering it off after sufficient warming but its no good, keeps dying out. maybe an idle adjustment is in order. another thing i noticed after running (with choke on) was that my #1 cylinder plug had turned black, while the #2 was white(didnt notice its color b4 i fired her up), could this be related to the air screws?

i know it sounds like a huge headache, but i got a screwed up bike solely for eduactional purposes, and im thoroughly enjoying getting stuck. thanks for the help guys.

[Suzuki mad]

OK, some basic here. Look at the carbs are they flat topped or domed topped. If you have a vacuum tap it should be flat topped.

If you put a 4-1 exhaust and individual filters its normall to up jet the carbs but its a bit of trial an error on sizing. Normally people pay lots to go on a dyno to check it but at £150 a run here in the UK its a little expensive.

Fuel flows into no 2 carb and then via a link pipe to the other carbs, therefore NO2 would get the full amount of fuel first so if the petcock was duff/naff/broken the other would get less fuel. Yes being white could be down to the air screws but its a little early to say at present.

You may also find that the PO has put in hotter or colder plugs to help set the bike up.

Was it laid up or stood before you got it?

As for the choke you should be able to put it on, start the engine and run for a shortwhile then take it off and the bike will run at tickover (qbout 1000-1200 rpm) comfortably than bog down and die. At the bottom airbox side of the carbs should be a small knurled nut between no 2 and 3 carb that will adjust the tickover up or down. You COULD play with that to get her running without choke but not for too long as if you're running lean you could be doing more damage to the engine. (ENGINE STRIP DOWN YIPPEEEE.)

Suzuki mad